The court will reduce unreasonably high contractual penalty

Employers should properly adjust and individualize the amount of contractual penalties in contracts with their employees. If the court finds that the penalty is excessive, it may be reduced accordingly. However in practice, reduction of contractual penalties in labour cases is rare. It is difficult to prove that a given penalty is excessive (leaving aside extreme situations). – Bartosz Tomanek and Maja Konopa comment for Rzeczpospolita.

The article in Polish is avialible here.